Highly pressure-proof abrasion resistant synthetic resin hoses have been used for, e.g., conveyance or transport of powdery or granular particles, and suction and compression-transport of iron powder, sand, ballast. As such synthetic resin hose, Japanese Patent Application Laid-Open No. 141753/1999 (JP-A-11-141753) discloses an abrasion resistant hose comprising an inner layer mainly formed with a polyester-series thermoplastic polyurethane resin, an outer protective layer (hose wall) comprising a soft vinyl chloride resin united with the inner layer by thermal-fusion, and a spiral reinforcement comprising a hard vinyl chloride resin buried in or attached to the outer protective layer.
For improving the moldability or processability of thermoplastic polyurethane resins by making them softer, the inner layer of the above-described abrasion resistant hose is generally formed with an externally-plasticized polyester-series thermoplastic polyurethane resin comprising a polyester-series thermoplastic polyurethane resin and a conventional plasticizer (e.g., a phthalate-series plasticizer) (e.g., E670MNAT manufactured by Nippon Miractran, Co. Ltd.); C70A10W manufactured by Takeda Badische Urethane Industrird, Ltd.).
However, when a powdery substance (e.g., powders or particles capable of absorbing or capturing plasticizer, such as slaked lime or active carbon) are passed through the inside of the abrasion resistant hose, there occurs a phenomenon that the plasticizer (e.g., a phthalate-series plasticizer) added to the thermoplastic polyurethane resin bleeds out from the inner layer to the outer and drained off as the powdery substance is being conveyed because the migration of the platicizer is large. Accompanying or being indifferent to such phenomenon, the conventional plasticizer of large migration, such as a phthalate-series plasticizer [e.g., dioctyl phthalate (DOP)], contained in the soft vinyl chloride resin forming the outer layer migrates to the adjoining inner layer. Therefore, the volume or size of the hose is reduced and the hose contracts, resulting in the hose which is now shorter than as it was.